Thornwaldt cyst (Tornwaldt cyst) is a congenital benign cystic lesion located in the midline of the posterior nasopharyngeal wall. It embryologically originates from the notochordal remnant (bursa pharyngealis) — developing from the distal tip of the primitive notochord that remains attached to the nasopharyngeal mucosa and fails to regress. Prevalence is reported as 3-7% in autopsy series. It is usually incidentally detected between ages 15-40 and the vast majority are asymptomatic. Symptomatic cases may present with nasal obstruction, posterior nasal drip, halitosis, and rhinolalia. On CT, it appears as a well-defined hypodense cystic lesion in the posterior midline nasopharynx. On MRI, T1 hyperintense signal due to proteinaceous/mucinous content is a diagnostic clue. Absence of enhancement excludes malignancy. Differentiation from nasopharyngeal carcinoma is critically important — absence of solid component, no enhancement, midline location, and no bone erosion support benignity.
Age Range
15-70
Peak Age
40
Gender
Equal
Prevalence
Uncommon
Thornwaldt cyst results from the cranial tip of the primitive notochord remaining attached to the nasopharyngeal mucosa during embryological development. In normal development, the distal end of the notochord (bursa pharyngealis) completely regresses. When regression fails, an epithelium-lined cyst forms around the notochordal remnant. The cyst lumen is lined by respiratory or squamous epithelium and contains proteinaceous/mucinous fluid. This proteinaceous content causes T1 shortening (T1 hyperintensity) on MRI — the paramagnetic effect of proteins accelerates T1 relaxation of water molecules. Because the cyst wall is thin and avascular, it shows no enhancement — this feature provides clear differentiation from solid neoplasms. In infected Thornwaldt cyst, mild rim enhancement may be seen due to wall inflammation but no solid component forms. The midline location of the cyst reflects the midline developmental pathway of the notochord — a paramedian cyst questions the Thornwaldt diagnosis.
A well-defined cystic lesion in the posterior midline nasopharynx that is T1 hyperintense, T2 hyperintense, and non-enhancing is the signature finding of Thornwaldt cyst. T1 hyperintensity results from proteinaceous cyst content shortening T1 relaxation of water molecules. This triple combination (midline + T1 hyperintense + no enhancement) diagnoses Thornwaldt cyst with high reliability.
Well-defined cystic lesion in the posterior midline nasopharynx showing T1 hyperintense signal. Appears T1 hyperintense due to proteinaceous or mucinous cyst content. This feature is the most important distinguishing finding from simple cysts (T1 hypointense). Size typically 5-10 mm, rarely exceeds 20 mm.
Report Sentence
A well-defined cystic lesion measuring ___ mm in the posterior midline nasopharynx showing T1 hyperintense signal is identified, consistent with Thornwaldt cyst with proteinaceous content.
T2 hyperintense signal — consistent with cyst fluid content. Most Thornwaldt cysts appear bright on T2. However, T2 signal may be variable (isointense or even hypointense) in cysts containing high protein concentration or old blood products. The T1 hyperintense + T2 hyperintense combination is characteristic of proteinaceous cyst.
Report Sentence
The lesion demonstrates T2 hyperintense signal consistent with cystic/fluid content.
No enhancement on contrast-enhanced MRI — no gadolinium uptake due to avascular cyst wall and absence of solid component. This finding reliably excludes malignancy. Thin rim enhancement may suggest infection/inflammation but solid nodular enhancement should never be seen.
Report Sentence
The lesion shows no enhancement on contrast-enhanced sequences, interpreted as favoring benign cystic lesion (Thornwaldt cyst) with absence of solid component.
Well-defined hypodense cystic lesion (0-20 HU) in the posterior midline nasopharynx. The cyst is of fluid density, with thin and smooth wall. No calcification, bone erosion, or infiltration of surrounding tissues. Midline location and cystic structure on CT suggest Thornwaldt cyst diagnosis, but MRI confirmation is recommended.
Report Sentence
A well-defined hypodense cystic lesion measuring ___ mm (___ HU) is identified in the posterior midline nasopharynx, consistent with Thornwaldt cyst; no enhancement or bone erosion is detected.
No diffusion restriction on DWI — water molecules move freely in cyst fluid. This finding supports differentiation from malignant solid lesions (NPC, lymphoma). ADC value is high (>2.0 × 10⁻³ mm²/s). An infected cyst may show diffusion restriction due to viscous purulent content — pattern similar to abscess.
Report Sentence
The lesion demonstrates no diffusion restriction on DWI, consistent with benign cystic lesion.
Criteria
Incidentally detected, small (<10 mm), asymptomatic cyst. Most commonly encountered form.
Distinct Features
No treatment required, follow-up not mandatory. Mentioned in radiological report to avoid unnecessary biopsy.
Criteria
Cyst causing nasal obstruction, posterior nasal drip, halitosis, or chronic nasopharyngitis symptoms. Usually >10 mm.
Distinct Features
Treatment with endoscopic marsupialization. MRI findings identical to asymptomatic form — size difference and symptom presence determine diagnosis.
Criteria
Cyst infection — fever, pain, nasopharyngeal swelling. Rare complication.
Distinct Features
Thin rim enhancement may be seen on MRI (wall inflammation), diffusion restriction possible on DWI due to viscous purulent content. Antibiotics + drainage if needed.
Distinguishing Feature
NPC is solid mass, enhances, infiltrative, bone erosion; Thornwaldt is cystic, no enhancement, midline, no bone erosion
Distinguishing Feature
Adenoid hypertrophy is diffuse tissue thickening, solid, enhancing; Thornwaldt is focal cystic lesion, non-enhancing
Distinguishing Feature
Lymphoma is solid mass, marked DWI restriction, enhancing; Thornwaldt is cystic, no DWI restriction, non-enhancing
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upThornwaldt cyst is a benign congenital lesion; asymptomatic cysts require no treatment or follow-up. Diagnosis is made by MRI findings (T1 hyperintense, non-enhancing midline cyst) — biopsy is not needed. Identification in radiological reports to avoid unnecessary biopsy is the most important clinical contribution. Symptomatic cysts (5-10%) are treated with endoscopic marsupialization — low recurrence rate.
Thornwaldt cyst is a benign congenital lesion that does not require treatment. Asymptomatic incidental cysts require no intervention beyond recognition. Symptomatic cysts (nasopharyngeal obstruction, chronic nasopharyngitis) are rare and treated with endoscopic marsupialization. Its most important clinical significance is differentiation from nasopharyngeal carcinoma.